Showing papers by "Georg N. Duda published in 2003"

Proximal humeral fractures: how stiff should an implant be? A comparative mechanical study with new implants in human specimens.

Abstract: Background The objective of this study was to determine the in vitro characteristics of the clinically used and newly developed implants for the stabilization of proximal humeral fractures under static and cyclic loading. The goal was to optimize implant stiffness for fracture stabilization even in weak bone stock.

Where should implants be anchored in the humeral head

Abstract: To determine histomorphometric and bone strength distribution of the proximal humerus, analyses were done on 24 freshly harvested human cadaveric humeri. Median ages of 46 and 69 years were recorded respectively for the male group (n = 11; minimum, 34 years; maximum, 76 years) and the female group (n = 13; minimum, 46 years; maximum, 90 years). The humeral head was sliced into four equal horizontal levels (Levels 1-4). Five regions of interest were defined in each cutting plane: anterior, posterior, lateral, medial, and central. Histomorphometric analyses evaluated structural parameters (tissue volume to bone volume ratio, trabecular thickness), connectivity (number of nodes, node to node length), and trabecular orientation (mean bone length). The peak values of histomorphometric parameters and bone strength were identified for the cranial section and decreased caudally. The medial and dorsal aspects of the proximal humeral head were found to be the areas of highest bone strength. The trabecular network formed a pattern that connected the center of the gleaned cavity. The structural and connectivity parameters, bone strength, and trabecular orientation showed region- and level-related characteristics. Knowledge of distribution, microstructure, and quality of bone in the humeral head allows the remaining bone stock to be used effectively, even in elderly patients, with a minimally invasive approach and maximum mechanical stability.

Interfragmentary movements in the early phase of healing in distraction and correction osteotomies stabilized with ring fixators

Abstract: Experimental analyses have demonstrated the impact of mechanical conditions on bone healing. In critical clinical cases the mechanical conditions may be even more demanding than those in experimental studies. This study set out to examine the gap movements in distraction and correction osteotomies and to determine the suitability of initial fixation. Interfragmentary movements, ground reaction forces, and stability (ground reaction force divided by interfragmentary movement) were measured in 18 patients with tibial osteotomies stabilized by Ilizarov hybrid constructs until either bone union or conversion to internal fixation occurred (9 distraction treatments, 9 correction osteotomies). Consolidation was determined by clinical evaluation and standard radiographic techniques. In both groups cocontraction led to gap movements comparable to level walking. Although the in vitro stiffness was slightly increased in the correction constructs, the interfragmentary movement in vivo was initially comparable between the groups. Patients undergoing distraction returned later to full weight bearing than patients undergoing correction treatment. In the correction group the stability increased with treatment time, while in the distraction group the stability remained relatively small. The in vivo mechanical conditions in challenging clinical cases appear far more demanding than those in experimental studies. In distraction, mechanical conditions at the defect appear to be more critical than during correction osteosynthesis. According to the persistence of shear motion, even after 80 days of treatment, it may from the clinical point of view be important to maintain interfragmentary compression during the whole healing process and thereby reduce shear.

The influence of alignment on the musculo-skeletal loading conditions at the knee

Abstract: Background and aim High tibial osteotomies attempt to recreate physiologically normal joint loading. Previous studies have discussed the influence of mal-alignment on the distribution of static loads to the medial and lateral compartments of the knee. The aim of this study was to determine the influence of mal-alignment on the tibio-femoral loading conditions during dynamic activities.

The influence of walking speed on kinetic and kinematic parameters in patients with osteoarthritis of the hip using a force-instrumented treadmill and standardised gait speeds

Abstract: It is difficult to identify objective parameters for assessing the joint function when dealing with the evaluation of orthopaedic procedures, especially endoprosthetic hip replacement. Clinical gait analysis enables parameters of force and movement to be quantified. However, the influence of gait speed on these parameters has hardly been taken into consideration so far. The objective of the present study was therefore to investigate the effect of gait speed on gait parameters and to simplify the clinical conditions in patients with osteoarthritis of the hip by determining a standardised gait speed. A total of 28 patients with severe unilateral osteoarthritis of the hip were investigated at different gait speeds. The gait analysis equipment used consisted of an infinitely adjustable treadmill with force plates and an infrared video system. A special control mechanism permitted adjustment of the treadmill speed to a patient's self-determined pace. The mean gait speed of all patients with osteoarthritis of the hip was set at 2.20 km/h (0.61 m/s). Eight of the 10 gait parameters assessed increased significantly with changing gait speed. Pathological changes in gait patterns were found at the three gait speeds investigated, with the changes more accentuated at higher speeds. Dependence of gait parameters on gait speed could be concluded for a group of patients and for control subjects. Use of a force-instrumented treadmill is necessary for the setting of a standard gait speed, which should be set as high as achievable by patients without inducing pain and problems of coordination or balance. With the usage of standardised speeds, clinical gait analysis becomes easier to perform. Furthermore, one can assess the expected biomechanical advantages of newer prostheses, thus providing the surgeon with a basis for further decisions.

Temporal profile of microvascular disturbances in rat tibial periosteum following closed soft tissue trauma.

Abstract: Bone devascularization due to impaired periosteal perfusion following fracture with severe soft tissue trauma has been proposed to precede and underlie perturbed bone healing. The extent and temporal relationship of periosteal microcirculatory deteriorations after severe closed soft tissue injury (CSTI) are not known. We hypothesized that periosteal microcirculation is adversely affected and the manifestation of trauma-initiated microvascular impairment in periosteum is substantially prolonged following CSTI. Using the controlled-impact injury device, we induced standardized CSTI in the tibial compartment of 35 isoflurane-anesthetized rats. Following the trauma the rats were assigned to five groups, differing in time of analysis (2 h, 24 h, 48 h, 1 and 6 weeks). Non-injured rats served as controls. Before the metaphyseal/diaphyseal periosteum was surgically exposed, intramuscular pressure within tibial compartment was measured. Using intravital fluorescence microscopy (IVM) we studied the microcirculation of the tibial periosteum. We calculated the edema index (EI) by measuring the skeletal muscle wet-to-dry weight ratio (EI = injured limb/contralateral limb). Microvascular deteriorations of periosteal microhemodynamics caused by isolated CSTI were reflected by persistent decrease in nutritive perfusion, markedly prolonged increase in microvascular permeability associated with increasingly sustained leukocyte rolling and adherence throughout the entire study period, mostly pronounced 48 h after the trauma. Peak level in capillary leakage coincided with the maximum leukocyte adherence, tissue pressure, and edema. Microcirculation of tibial periosteum in control rats demonstrated a homogeneous perfusion with no capillary or endothelial dysfunction. Isolated CSTI in absence of a fracture exerts long-lasting disturbances in periosteal microcirculation, suggesting a delayed temporal profile in manifestation of CSTI-induced periosteal microvascular dysfunction and inflammation. These observations may have therapeutic implications in terms of preserving periosteal integrity and considering the interaction of skeletal muscle damage and periosteal microvascular injury during management of musculoskeletal trauma.

Does partial weight bearing unload a healing bone in external ring fixation

Abstract: Partial weight bearing is thought to unload and protect the healing bone. Until now, there has been no objective method of assessing the amount of weight placed on the healing zone by the patient. The goal of this study was to determine the effects of partial weight bearing on the loading of the healing bone in tibial osteotomies. Six patients with complex tibial osteotomies, stabilized with Ilizarov ring fixator constructs, took part in this study. Three-dimensional interfragmentary movements were measured with reflective markers that were attached to the Schanz screws of the fixator. Patients were asked to rest, to co-contract the musculi gastrocnemii, to stand up, to walk slowly and to load partially the affected limb with 20 kg of weight. Compared with co-contraction, ground reaction forces of partial weight bearing, standing up and walking were significantly increased (P >0.05). Partial weight bearing did not unload the defect zone. No direct relationship between interfragmentary movement magnitudes and ground reaction forces was identified. Therefore, the concept of partial weight bearing cannot reliably reduce loading of a healing zone. It may, however, help to prevent patients from undergoing critical situations, such as stumbling, by increasing their general awareness.

Dose-dependent effects of combined IGF-I and TGF-β1 application in a sheep cervical spine fusion model

Abstract: Combined IGF-I and TGF-β1 application by a poly-(D,L-lactide) (PDLLA) coated interbody cage has proven to promote spine fusion. The purpose of this study was to determine whether there is a dose-dependent effect of combined IGF-I and TGF-β1 application on intervertebral bone matrix formation in a sheep cervical spine fusion model. Thirty-two sheep underwent C3/4 discectomy and fusion. Stabilisation was performed using a titanium cage coated with a PDLLA carrier including no growth factors in group 1 (n=8), 75 µg IGF-I plus 15 µg TGF-β1 in group 2 (n=8), 150 µg IGF-I plus 30 µg TGF-β1 in group 3 (n=8) and 300 µg IGF-I plus 60 µg TGF-β1 in group 4 (n=8). Blood samples, body weight and temperature were analysed. Radiographic scans were performed pre- and postoperatively and after 1, 2, 4, 8, and 12 weeks. At the same time points, disc space height and intervertebral angle were measured. After 12 weeks, the animals were killed and fusion sites were evaluated using quantitative computed tomographic (CT) scans to assess bone mineral density, bone mineral content and bony callus volume. Biomechanical testing was performed and range of motion, and neutral and elastic zones were determined. Histomorphological and histomorphometrical analysis were carried out and polychrome sequential labelling was used to determine the time frame of new bone formation. In comparison to the group without growth factors (group 1), the medium- and high-dose growth factor groups (groups 3 and 4) demonstrated a significantly higher bony callus volume on CT scans, a higher biomechanical stability, an advanced interbody bone matrix formation in histomorphometrical analysis, and an earlier bone matrix formation on fluorochrome sequence labelling. Additionally, the medium- and high-dose growth factor groups (groups 3 and 4) demonstrated a significantly higher bony callus volume, a higher biomechanical stability in rotation, and an advanced interbody bone matrix formation in comparison to the low-dose growth factor group (group 2). No significant difference could be determined between the medium- and the high-dose growth factor groups (groups 3 and 4, respectively). The local application of IGF-I and TGF-β1 by a PDLLA-coated cage significantly improved results of interbody bone matrix formation in a dose-dependent manner. The best dose-response relationship was achieved with the medium growth factor dose (150 µg IGF-I and 30 µg TGF-β1). With an increasing dose of these growth factors, no further stimulation of bone matrix formation was observed. Although these results are encouraging, safety issues of combined IGF-I and TGF-β1 application for spinal fusion still have to be addressed.

Mechanische grenzindikationen der unaufgebohrten marknagelung

Abstract: The extended usage of unreamed tibial nailing resulted in reports of an increased rate of complications, especially for the distal portion of the tibia. The goal was to gain a thorough understanding of the load-sharing mechanism between unreamed nail and bone in a fractured tibia, and to identify borderline indications due to biomechanical factors. In finite element analyses of a human tibia, horizontal defects were modeled using unreamed nailing for five different fracture locations, including proximal and distal borderline indications for this treatment method. The findings of this study show that with all muscle and joint contact forces included, nailing leads to considerable unloading of the interlocked bone segments. Unreamed nailing of the distal defect results in an extremely low axial and high shear strain between the fragments. Apart from biological reasons, clinical problems reported for distal fractures may be due to the less favorable mechanical conditions in unreamed nailing. From a biomechanical perspective, the treatment of distal tibial shaft fractures with unreamed nailing without additional fragment contact or without stabilizing the fibula should be carefully reconsidered.

Simulation method for musculo-skeletal loading of patient for use in surgical intervention and/or rehabilitation using individual musculo-skeletal parameters for determination of musculo-skeletal strains

Abstract: The method simulates the musculo-skeletal loading of a patient using the individual musculo-skeletal parameters of the patient, obtained by automatic measurement of anthropometric parameters and/or the position and/or alignment of joints, with computer-aided evaluation of the musculo-skeletal strains with respect to the contact forces or the degree of movement of a joint, or the fragment movement of a fracture. Also included are Independent claims for the following: (a) a device for evaluating the muscolo-skeletal loading of a patient; (b) a movement analysis system; (c) a navigation system for computer-controlled surgery.